A striking anomaly has been detected on the eastern side of the Great Pyramid at Giza, Antiquities Minister Mamdouh el-Damaty said on Monday.

The announcement comes at the end of a two-week project to scan Egypt’s main pyramids in order to identify the presence of unknown internal structures and cavities.

Called Scan Pyramids, the study is in its first stage and is carried out by a team from Cairo University’s Faculty of Engineering and the Paris-based organization Heritage, Innovation and Preservation under the authority of the Egyptian Ministry of Antiquities.

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The project uses a mix of technologies such as infrared thermography, muon radiography, and 3-D reconstruction to look inside four pyramids, which are more than 4,500 years old. They include Khufu, or Cheops, Khafre or Chephren at Giza, the Bent pyramid and the Red pyramid at Dahshur.

Several thermal anomalies were observed in all the monuments, but one remarkable anomaly was detected in the Great Pyramid, known as Khufu or Cheops.

“This anomaly is really quite impressive and it’s just in front of us, at the ground level,” Mehdi Tayoubi, founder of the Paris-based Heritage Innovation Preservation Institute, told Discovery News.

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Thermal measurements were carried out at different times in order to observe the pyramids during their warm-up phase from early morning until sunrise and during their cooling phase from late afternoon until sun set and early night.

“In cooling phase, the heat transfer is usually happening from the inside to the outside; while in heating phase, it is the opposite,” the researchers said.

They noted that if an object is built with blocks of the same material and has an identical “heat emissivity,” no significant temperature differences are detected.

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On the contrary, if there are heterogeneities in the structure, such as cavities or different type of material used in the construction, temperature differences are detected since some parts heat up or cool down faster due to difference in “heat emissivity.”

The Great Pyramid showed striking thermal differences.

Temperature differences detected between two adjacent stones from limestone of different qualities usually range from 0.1 to 0.5 degrees.

But Tayoubi’s team detected at the ground level of the Cheops pyramid, on the eastern side, an area of few blocks that had a 6-degree gap with neighboring blocks.

“This anomaly is impressive and obvious. We have several hypothesis but no conclusion for the moment,” Tayoubi said.

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Anomalies in thermal measurements can be explained by the presence of cavities, internal air currents, or different materials with specific thermal capacity.

All anomalies detected will be subject to further analysis, the researchers said.

“We need now to build models and thermal simulations to test different hypotheses in order to understand what we have found,” Tayoubi said.

The next steps of the project, which is scheduled to last over a year, will involve long term infrared survey of all the monuments.